1. Field of the Invention
The present invention relates generally to an apparatus and process for applying pesticides and other agents and materials to agricultural crops, vines, trees and vegetation.
2. Description of the Related Art
Insecticides and other agents are commonly applied to crops and other types of vegetation using a variety of techniques, including tunnel sprayers. In a conventional tunnel sprayer, a tractor is used to pull or push a spray rig apparatus such as is disclosed in U.S. Pat. No. 4,893,755 issued to J. Phillip Keathley ("Keathley"). In sprayers, similar to Keathley, a canopy or tunnel is formed around a segment of crops or vegetation. A spraying apparatus is then used to inject the desired agent into the confined canopy area. The canopy avoids, to some extent, drift of the agent away from the desired site of application. It is also known to use troughs within a tunnel sprayer canopy to recover and recirculate agent which has deposited on the inner walls of the canopy.
Conventional tunnel sprayers deposit aerosol particles of an agent on crops by spraying the agent directly on to the crops. Thus, existing sprayers known in the art rely on the kinetics of the aerosol particles. There are several mechanisms and effects at work in such an aerosol environment. The principle factor is the droplet size in the aerosol spray. The larger the droplets, the less the surface area on the droplets for a given amount of spray, and the less loss to evaporation. This would seem to favor large droplets. However, other effects then come into play.
If a relatively small number of large droplets are used to coat a plant, there will have to be significant overcoverage to insure that the plants are wetted. This means that some areas of the plant surface will receive excessive pesticide to insure complete coverage, and thus the application will be inefficient. In addition, the possibility of both excessive droplet size and precipitation from collision is greatly increased with larger initial droplet sizes.
If, in a conventional sprayer, the droplets are too small, there will be much greater surface area for a given volume of spray, and there will be excessive evaporation and drift. Given these two conflicting effects, the tendency for spray applications has been to use the largest droplets consistent with efficient coverage. The majority of sprays are applied well in excess of 40 microns for field applications. While the tunnel sprayer limits some of the drift problems, it does not eliminate the conflicting requirements of droplet size and application.
Additional constraints are presented by the requirements for bringing the droplets into contact with the plants. There has been much study of the impact mechanism whereby droplets wet a surface. A collision between aerosol droplets and a surface such that they wet a surface is referred to in the literature as an "effective" collision. There are a large number of factors that influence the mechanism but the size of droplets was found to have an appreciable effect. In a study by Hartley and Brunskill, Surface Phenomena in Chemistry and Biology, Permagon Press (1958) collisions on pea leaves were effective when the droplet size was less than 50 microns, and ineffective when greater than 125 microns. On rough surfaces of the plant, the effect was largely independent of the angle of impact.
In a conventional sprayer, the small droplets in the aerosol mix would lose velocity rapidly and would drift in the atmosphere and would either coagulate into larger droplets, or evaporate and become water vapor. However, the larger droplets would require greater numbers of impacts to produce effective coverage of the plant, and higher velocities.
The other major factor affecting the ability of the droplets to have effective collisions with the plant surface is the wetting of the surface itself. It has been shown in studies by McCully that when particles or the surface are rendered hydrophobic, the effectiveness of collisions is significantly decreased. (McCully, C, et al., Ind. Eng. Chem., 48, 1512 (1956), as referenced in Fuchs, et al, The Mechanics of Aerosols, Dover Press (1989).) The influence of wettability is greatly increased when the kinetic energy of the collisions is low. In the past, pesticide application has relied on high kinetic energy either by the use of large droplets or large droplets in conjunction with high velocity. Thus, the ideal state would be to have high wettability and low kinetic energy while still maintaining the effectiveness of collision.
Conventional tunnel sprayers known in the art provide neither of the two conditions, high wettability and low kinetic energy, required for ideal application of pesticide agents to crops. As seen in U.S. patent application No. 2,977,715 issued to M. E. Lindsay ("Lindsay") the agent is randomly deposited on the leaves of the vegetation by velocity impingement of the spray onto the vegetation. Lindsay teaches spraying agent into a column of air and then impinging the air column upon plant foliage at an increased velocity. Although Lindsay discloses spraying the aerosol agent into a duct before blowing the air column into the canopy, Lindsay does nothing to change the aerosol environment. Thus, the conditions identified above which produce the best application of the agent are absent from Lindsay.
Conventional devices control the force of impingement by the pressure supplied by blowers. In devices such as Lindsay, the air discharge is at a substantial velocity such that it causes agitation of the plants; however, because such spray rigs rely on impingement velocity, they do not always apply the agents evenly on the vegetation. Second, more agent than would be desired is deposited on the ground beneath the plants. These factors increase the financial and environmental costs of operating such devices because large quantities of pesticide agents are required and wasted.
In addition to providing inefficient and ineffective coverage of the agent on the target crops, the conventional devices are further disadvantageous because their method of application results in shingling. Shingling occurs when the force of the spray or air is so strong that the leaves of the crops press against each other. The result is that one leaf covers all or a portion of the leaf which is behind it, thereby preventing coverage of both leaf surfaces. This phenomenon is inherent in the conventional tunnel sprayers because the high velocity required to impinge the large aerosol particles against the crops.
As a result of the above factors, the problem facing the development of a more efficient method and apparatus for the application of agents to crops is to integrate a variety of conflicting requirements involving evaporation, droplet size, inertia of particles, wettability of surfaces and design of a suitable apparatus.
A further problem associated with the use of tunnel sprayers is the turning radius required to turn the tunnel sprayer around in the headland area. The headlands are minimized to increase the percentage of land utilizable for planting; thus, there is a limited turning radius. Therefore, minimal space at the end of a row of crops is provided. Tractors pulling the conventional sprayer, especially tunnel sprayers, cannot be used or are used with difficulty in such areas. Thus, it is desirable to minimize the turning radius of the tractors used in spraying operations and the equipment which they pull.
It is therefore an object of this invention to provide a more efficient and cost effective method and apparatus for applying agents to crops, vegetation, and trees, while avoiding the problems associated with conventional impingement velocity tunnel sprayers.
Another object of the invention is to utilize a process which will create a large number of effective collisions while nevertheless operating with comparatively low velocities.
Yet another object of this invention is to provide an apparatus and method which will decrease the operation costs of applying agents by maximizing the actual deposition of agents to the crops.
A still further object of the invention is to reduce wasted pesticide agents due to evaporate loss in the deposition process by the means of application and recapture from within the apparatus for reapplication to the crops.
A still further object of the present invention is to minimize the turning radius required for the tractor when pulling a tunnel sprayer.